The present invention relates to an apparatus for supplying powder. More particularly, the present invention relates to an apparatus for supplying stored powder to, for example, a transportation path.
The prior art will be described, wherein a toner hopper is used in the developing unit of a copying machine, for example.
The developing unit of a copying machine has a toner hopper (referred to as hopper below) for storing supply toner. As disclosed in U.S. Pat. No. 4,436,411, a hopper thereof usually has a bottom portion which is V-shaped in a sectional side view, formed by sloping inner surfaces. The stored toner moves down along the inner surfaces to the bottom portion. Then, as described in U.S. Pat. No. 4,803,513 and U.S. Pat. No. 4,422,750, the toner is transported further down, to the casing of the developing unit, by the rotation of a supply roller provided in the bottom part of the hopper.
With respect to the volume of the stored toner, a more moderate slope of the inner surfaces is preferred. This is due to the fact that a hopper having more gently sloping surfaces can contain a greater amount of toner. However, should the angles of the slopes be too reduced, toner in the hopper may not fall, wherein the toner would remain in the hopper and, furthermore, may deteriorate. At the same time, if the slopes of the hopper have too great an angle, the hopper can contain only a small amount of toner, though the toner does readily drop. Furthermore, the toner may form a bridge in a hopper having very steep slopes. The bridge causes a gap between the bulk of toner to be supplied and the supply roller, thereby interrupting the toner supply.
In order to improve the operation efficiency in exchanging the developing device, Japanese Patent Laying-Open No. 22367/1986 discloses a developing unit which comprises a developing device and a hopper separate from the developing device. This separable type developing unit must have transportation means in the hopper for transporting toner to a connection path between the hopper and the developing device. The transportation means usually consists of a rotatable member such as a spiral. Moreover, it may be presumed that if the rotating spiral agitates the toner, there would be little toner remnant in a hopper having moderate slopes inside for storing a greater amount of toner.
Such problems concerning the slope angles in a hopper, or problems concerning the contradiction with regard to the volume of stored powder as against remnant powder in the container, may occur not only in a toner hopper for use in the developing unit, but also in various other kinds of hoppers for storing other kinds of powder.
As briefly described in the above, a developing unit having a developing device and a hopper separate from the developing device to improve operation efficiency has been proposed. In this unit, the hopper may be designed for placement in a suitable position. However, wherein the hopper and the developing device are disposed far from each other, a long toner transportation path, such as a pipe, must be provided. Such a structure requires an opening in the bottom or a side of the hopper to supply toner to the transportation path.
However, if too large an amount of toner is supplied through the opening to the transportation path, an over-supply problem and/or a toner-spreading problem can occur. Furthermore, if the opening is formed in a side wall of the hopper, a bulk of the toner which is the farthest from the opening in the opposite side wall must be transported to the opening over some distance, so that the toner may become adhered to the inside wall of the hopper en route, due to its longer residence.
These problems may occur not only in toner supply apparatuses of copying machines but also in other kinds of powder supply apparatuses in which powder drops through an opening.